Flow and Mass Transfer in Bends Under Flow-Accelerated Corrosion Wall Thinning Conditions

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
John M. Pietralik ◽  
Chris S. Schefski
Keyword(s):  
Mass Transfer ◽  
Water Chemistry ◽  
Nuclear Power ◽  
Flow Conditions ◽  
Transfer Coefficients ◽  
Ferrous Ions ◽  
Local Flow ◽  
Accelerated Corrosion ◽  
Flow Accelerated Corrosion

The three groups of parameters that affect flow-accelerated corrosion (FAC) are the flow conditions, water chemistry, and materials. Nuclear power plant (NPP) data and laboratory tests confirm that, under alkaline water chemistry, there is a close relationship between local flow conditions and FAC rates in the piping components. The knowledge of the local flow effects can be useful for developing targeted inspection plans for piping components and predicting the location of the highest FAC rate for a given piping component. A similar evaluation applies also to the FAC in heat transfer equipments such as heat exchangers and steam generators. The objective of this paper is to examine the role of the flow and mass transfer in bends under alkaline FAC conditions. Bends experience increased FAC rates compared with straight pipes, and are the most common components in piping systems. This study presents numerical simulations of the mass transfer of ferrous ions and experimental results of the FAC rate in bends. It also shows correlations for mass transfer coefficients in bends and reviews the most important flow parameters affecting the mass transfer coefficient. The role of bend geometry and, in particular, the short and long radii, surface roughness, wall shear stress, and local turbulence, is discussed. Computational fluid dynamics calculations and plant artifact measurements for short- and long-radius bends are presented. The effect of the close proximity of the two bends on the FAC rate is also examined based on CANDU (CANDU is a registered trademark of the Atomic Energy of Canada Limited) NPP inspection data and compared with literature data.

Flow and Mass Transfer in Bends Under Flow-Accelerated Corrosion Wall Thinning Conditions

2009 ◽  
Author(s):  
John M. Pietralik ◽  
Chris S. Schefski
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Flow Conditions ◽  
Ferrous Ions ◽  
Local Flow ◽  
Accelerated Corrosion ◽  
Flow Effects ◽  
Flow Accelerated Corrosion

The three groups of parameters that affect flow-accelerated corrosion (FAC) are flow conditions, water chemistry, and materials. Nuclear power plant (NPP) data and laboratory tests confirm that under alkaline water chemistry there is a close relationship between local flow conditions and FAC rates in piping components. The knowledge of local flow effects can be useful for developing targeted inspection plans for piping components, predicting the location of the highest FAC rate for a given piping component, and determining what piping components should be replaced. A similar evaluation applies also to FAC in heat transfer equipment such as heat exchangers and steam generators. The objective of this paper is to examine the role of flow and mass transfer in bends under FAC conditions. Bends experience increased FAC rates compared to straight pipes, and are the most common components in piping systems. When the flow effects are dominant, the FAC rate is proportional to the mass flux of ferrous ions, which, in turn, is proportional to the mass transfer coefficient in the flowing water. The mass transfer coefficient describes the intensity of the transport of corrosion products (ferrous ions) from the oxide-water interface into the bulk water. Therefore, this parameter can be used for predicting the local distribution of the FAC rate. The current paper presents plant and laboratory evidence of the relationship between local mass transfer conditions and the FAC rate in bends. It shows correlations for mass transfer coefficients in bends and reviews the most important flow parameters affecting the mass transfer coefficient. The role of bend geometry and, in particular, the short and long radii, surface roughness, wall shear stress, and local turbulence is discussed. Computational fluid dynamics calculations and plant artefact measurements for short-radius and long radius bends are presented. The effect of the close proximity of two bends on FAC rate is also examined based on CANDU™ NPP inspection data and compared with literature data.

Validation of Code System DRAWTHREE-FAC for Evaluation of Wall Thinning due to Flow Accelerated Corrosion by PWR Feed Water Piping Analysis

2011 ◽  
Author(s):  
Masanori Naitoh ◽  
Shunsuke Uchida ◽  
Hidetoshi Okada ◽  
Seiichi Koshizuka
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Flow Behavior ◽  
Feed Water ◽  
Code System ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Flow Accelerated Corrosion

The code system DRAWTHREE-FAC for evaluation of pipe wall thinning due to flow accelerated corrosion was validated by comparison of calculations with measurements at the secondary piping of a PWR plant. Distributions of flow velocity and temperature along the whole piping were calculated with the system code RELAP5 and corrosive conditions were calculated by a N2H4-O2 reaction analysis code. Precise flow turbulence at major parts of the piping was analyzed with a 3D computational fluid dynamics (CFD) code to obtain mass transfer coefficients at structure surfaces. In the CFD calculation, the κ-ε method was applied. Since the κ-ε method can not give detailed flow behavior in a boundary layer, the results were extrapolated with a wall function, a power law, and analogy of non-dimensional numbers to obtain mass transfer coefficients in the boundary layer. Then, wall thinning rates were calculated by coupling models of static electrochemical and dynamic oxide layer growth. The wall thinning calculation was focused on T-junction portions of a PWR feed water line. The wall thickness of the PWR secondary piping was measured by the ultrasonic testing. The calculated residual wall thicknesses after thinning agreed with the measurements within ±20% difference.

Disturbed Flow and Flow-Accelerated Corrosion in Oil and Gas Production

1998 ◽  
Vol 120 (1) ◽  
pp. 72-77 ◽  
Author(s):  
K. D. Efird
Keyword(s):  
Mass Transfer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Oil And Gas ◽  
Steel Corrosion ◽  
Flow Conditions ◽  
Accelerated Corrosion ◽  
Disturbed Flow ◽  
Wall Shear ◽  
Flow Accelerated Corrosion

The effect of fluid flow on corrosion of steel in oil and gas environments involves a complex interaction of physical and chemical parameters. The basic requirement for any corrosion to occur is the existence of liquid water contacting the pipe wall, which is primarily controlled by the flow regime. The effect of flow on corrosion, or flow-accelerated corrosion, is defined by the mass transfer and wall shear stress parameters existing in the water phase that contacts the pipe wall. While existing fluid flow equations for mass transfer and wall shear stress relate to equilibrium conditions, disturbed flow introduces nonequilibrium, steady-state conditions not addressed by these equations, and corrosion testing in equilibrium conditions cannot be effectively related to corrosion in disturbed flow. The problem in relating flow effects to corrosion is that steel corrosion failures in oil and gas environments are normally associated with disturbed flow conditions as a result of weld beads, pre-existing pits, bends, flanges, valves, tubing connections, etc. Steady-state mass transfer and wall shear stress relationships to steel corrosion and corrosion testing are required for their application to corrosion of steel under disturbed flow conditions. A procedure is described to relate the results of a corrosion test directly to corrosion in an operation system where disturbed flow conditions are expected, or must be considered.

Flow Accelerated Corrosion in Single Bends Under Annular Two Phase Flow Conditions

2012 ◽  
Author(s):  
H. Mazhar ◽  
D. Ewing ◽  
J. S. Cotton ◽  
C. Schefski ◽  
C. Y. Ching
Keyword(s):  
Mass Transfer ◽  
Local Maximum ◽  
Outer Wall ◽  
Water Velocity ◽  
Maximum Mass ◽  
Flow Conditions ◽  
Air Velocity ◽  
Two Phase ◽  
Accelerated Corrosion ◽  
Flow Accelerated Corrosion

The distributions of the mass transfer coefficient in horizontal 90 degree bends were measured under a range of two phase annular flow conditions. A dissolving wall technique at a high Schmidt number (Sc = 1280) is used for the measurements. The maximum mass transfer occurred on the centerline of the bend outer wall at an angle of approximately 50 degrees from the bend inlet under all tested conditions. The area of maximum mass transfer was found to span approximately 30 degrees in the circumferential direction. A second region of enhanced mass transfer occurred on the latter part of the bend with a local maximum occurring slightly off the bend centerline in some cases. Changing the air and water superficial velocities (Jν = 20 to 30 m/s, JL = 0.17 to 0.41 m/s) showed that the air velocity had a larger effect on the mass transfer than the water velocity; however the effect of the water velocity on the mass transfer was not insignificant.

scholarly journals Predicting and Preventing Flow Accelerated Corrosion in Nuclear Power Plant

2014 ◽  
Vol 2014 ◽  
pp. 1-23 ◽  
Author(s):  
Bryan Poulson
Keyword(s):  
Mass Transfer ◽  
Nuclear Power ◽  
Mass Transfer Rate ◽  
Environmental Parameters ◽  
Theoretical Models ◽  
Carbon Steels ◽  
Accelerated Corrosion ◽  
Material Factor ◽  
Flow Accelerated Corrosion ◽  
Over 40 Years

Flow accelerated corrosion (FAC) of carbon steels in water has been a concern in nuclear power production for over 40 years. Many theoretical models or empirical approaches have been developed to predict the possible occurrence, position, and rate of FAC. There are a number of parameters, which need to be incorporated into any model. Firstly there is a measure defining the hydrodynamic severity of the flow; this is usually the mass transfer rate. The development of roughness due to FAC and its effect on mass transfer need to be considered. Then most critically there is the derived or assumed functional relationship between the chosen hydrodynamic parameter and the rate of FAC. Environmental parameters that are required, at the relevant temperature and pH, are the solubility of magnetite and the diffusion coefficient of the relevant iron species. The chromium content of the steel is the most important material factor.

Evaluation of Hydraulic Factors Affecting Flow Accelerated Corrosion and Its Verification With Power Plant Data

2009 ◽  
Author(s):  
Kimitoshi Yoneda ◽  
Taku Ohira ◽  
Kazuhiro Tanji ◽  
Shinji Akiba ◽  
Koichi Niiyama ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Chemical Effect ◽  
Transfer Coefficients ◽  
Pressurized Water ◽  
Accelerated Corrosion ◽  
Factors Affecting ◽  
Water Reactor ◽  
Eddy Simulation ◽  
Plant Data ◽  
Flow Accelerated Corrosion

Flow Accelerated Corrosion (FAC) is well known as a complex phenomana of hyraulics and electro-chemicals. Among the two, this study focused on the hydraulic factors affecting FAC. FAC experiments with small rectangular flow duct were conducted in PWR condensate condition. Flow field for the experiment was calculated with numerical simulation using LES (Large Eddy Simulation) turbulence model. From both experimental and numerical results, new model of mass transfer coefficient, as the essential parameters of hydraulics, was proposed considering local turbulent velocity, so as to evaluate the effect of eccentric flow on FAC. To verify the applicability of the model, FAC plant data of actual PWR (Pressurized Water Reactor) condensate line (146 degC) and BWR (Boiling Water Reactor) condensate line (35 degC) were referred. Mass transfer coefficients for each pipe lines were calculated from flow numerical analysis. The new proposed model showed good correlation with the data of FAC thinnng rate, and its applicability was confirmed. In addtion, comparing the two plant cases, electro-chemical effect could be estimated as a similar level, which suggests the possibility of low-temperature FAC in BWR condensate lines.

CFD Application to Flow-Accelerated Corrosion in Feeder Bends

2006 ◽  
Author(s):  
John M. Pietralik ◽  
Bruce A. W. Smith
Keyword(s):  
Mass Transfer ◽  
Mass Transport ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Oxide Layer ◽  
Operating Conditions ◽  
Local Flow ◽  
Accelerated Corrosion ◽  
Wall Functions ◽  
Flow Accelerated Corrosion

Feeder piping in CANDU® plants experiences a thinning degradation mechanism called Flow-Accelerated Corrosion (FAC). The piping is made of carbon steel and has high water flow speeds. Although the water chemistry is highly alkaline with room-temperature pH in a range of 10.0–10.5, the piping has FAC rates exceeding 0.1 mm/year in some locations, e.g., in bends. One of the most important parameters affecting the FAC rate is the mass transfer coefficient for convective mass transport of ferrous ions. The ions are created at the pipe wall as a result of corrosion, diffuse through the oxide layer, and are transported from the oxide-layer/water interface to the bulk water by mass transport. Consequently, the local flow characteristics contribute to the highly turbulent convective mass transfer. Plant data and laboratory experiments indicate that the mass transfer step dominates FAC under feeder conditions. In this study, the flow and mass transfer in a feeder bend under operating conditions were simulated using the Fluent™ computer code. Because the flow speed is very high, with the Reynolds numbers in a range of several millions, and because the geometry is complex, experiments in a 1:1 scale were conducted with the main objective to validate flow simulations. The experiments measured pressure at several key locations and visualized the flow. The flow and mass transfer models were validated using available friction-factor and mass transfer correlations and literature experiments on mass transfer in a bend. The validation showed that the turbulence model that best predicts the experiments is the realizable k-ε model. Other two-equation turbulence models, as well as one-equation models and Reynolds stress models were tried. The near-wall treatment used the non-equilibrium wall functions. The wall functions were modified for surface roughness when necessary. A comparison of the local mass transfer coefficient with measured FAC rate in plant specimens shows very good agreement. Visualization experiments indicate secondary flows in the bends. No boundary layer separation was observed in experiments or in simulations.

Flow and mass transfer downstream of an orifice under flow accelerated corrosion conditions

2012 ◽  
Vol 252 ◽  
pp. 52-67 ◽  
Author(s):  
Wael H. Ahmed ◽  
Mufatiu M. Bello ◽  
Meamer El Nakla ◽  
Abdelsalam Al Sarkhi
Keyword(s):  
Mass Transfer ◽  
Accelerated Corrosion ◽  
Flow Accelerated Corrosion
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